For convenience, the disclosure of the invention will be based on a hospital bed, as known e.g. from EP 498 111 B2 to J. Nesbit Evans & Co. Ltd., in which the mattress supporting face may be adjusted to a contour by at least two actuators, and in which the frame, in which the mattress supporting face is mounted, may be raised and lowered as well as titled over a transverse axis (Trendelenburg positions) by two additional actuators. For the operation of the bed, there is a handset for the patient, or, as an alternative or as a supplement, a control panel may be incorporated in the guard rail. Likewise, a separate handset as well as a control box (called an ACP) may be provided for the staff, mounted at the foot end of the bed where the staff may read all adjustment functions. All these units are connected by individual multi-conductor cables to a central control box (CB), also called a control unit containing a control, a power supply intended for connection to the mains as well as a rechargeable battery pack so that the bed may function temporarily without being connected to the mains. Another example of a bed is shown in WO 01/47340 to Hill-Rom Services, Inc. An example of a simple therapy couch is disclosed in U.S. Pat. No. 5,014,688 to Tri W-G, Inc.
The control typically comprises a microprocessor and associated software adapted to the individual bed makes and the specific intended uses of the beds.
With many different units in an actuator system, the wiring is quite complicated and must be established with great care in order to avoid overloading in the movable mechanical parts. Further, connection of ever more units is also required, e.g. an additional actuator for the adjustment of the neck support, a device for the automatic turning of the patients, devices for counteracting bedsores, massage devices, sophisticated air mattresses, etc.
Thus, there is a wish for many keys (functions) on the handsets as well as many handsets parallel in the system.
A traditional system is characterized in that there is a direct connection from any handset function to the control unit. It is not so that the handset functions can only be arranged in one physical unit; these may very well be distributed on several handsets connected in parallel, but understood in the sense that for each function there is a key (activation unit), and it is connected directly.
A key may refer to a wire or to a switch between two wires (matrix handsets).
In the first case, a maximum of 8 functions (1 common as well as 8 signals) may thus be achieved with a normal 9-conductor cable. With the matrix type, a maximum of 20 keys (4×5 lines) may be achieved using 9 conductors. Typically, however, one of the conductors is used for grounding, and, therefore, only a 4×4 matrix corresponding to 16 keys can be used. Matrix handsets unfortunately have the drawback that several keys cannot be detected with certainty at the same time, as there is no unique decoding as to which keys are activated.
US 2003/0079289 A1 describes an adjustable bed particularly intended for severely overweight patients. The bed may be controlled by serial signals, where adjustments are written in a plurality of RAM circuits, and where the contents are read and executed periodically, controlled by an interrupt. This is a relatively complicated control, which requires a good deal of special features, and which is relatively complex to implement and extend with additional functionalities.
U.S. Pat. No. 6,396,224 B1 and U.S. Pat. No. 5,600,214 A describe other control systems for adjustable beds. Again, complex solutions are involved, where just one unit can be active at a time.
A further drawback of the foregoing is that they are all based on master-slave communication. This requires that all units in the system are known in advance, since these must have individual addresses in connection with the design of the communication.